The maximum key description size is 4095. Commit f771fde82051
inadvertantly reduced that to 255 and made sizes between 256 and 4095 work
weirdly, and any size whereby size & 255 == 0 would cause an assertion in
__key_link_begin() at the following line:
BUG_ON(index_key->desc_len == 0);
This can be fixed by simply increasing the size of desc_len in struct
keyring_index_key to a u16.
Note the argument length test in keyutils only checked empty descriptions
and descriptions with a size around the limit (ie. 4095) and not for all
the values in between, so it missed this. This has been addressed and
https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/keyutils.git/commit/?id=066bf56807c26cd3045a25f355b34c1d8a20a5aa
now exhaustively tests all possible lengths of type, description and
payload and then some.
The assertion failure looks something like:
kernel BUG at security/keys/keyring.c:1245!
...
RIP: 0010:__key_link_begin+0x88/0xa0
...
Call Trace:
key_create_or_update+0x211/0x4b0
__x64_sys_add_key+0x101/0x200
do_syscall_64+0x5b/0x1e0
entry_SYSCALL_64_after_hwframe+0x44/0xa9
It can be triggered by:
keyctl add user
"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
a @s
Fixes: f771fde82051 ("keys: Simplify key description management")
Reported-by: kernel test robot <[email protected]>
Signed-off-by: David Howells <[email protected]>
cc: Linus Torvalds <[email protected]>
---
include/linux/key.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/include/linux/key.h b/include/linux/key.h
index 91f391cd272e..50028338a4cc 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -94,11 +94,11 @@ struct keyring_index_key {
union {
struct {
#ifdef __LITTLE_ENDIAN /* Put desc_len at the LSB of x */
- u8 desc_len;
- char desc[sizeof(long) - 1]; /* First few chars of
description */
+ u16 desc_len;
+ char desc[sizeof(long) - 2]; /* First few chars of
description */
#else
- char desc[sizeof(long) - 1]; /* First few chars of
description */
- u8 desc_len;
+ char desc[sizeof(long) - 2]; /* First few chars of
description */
+ u16 desc_len;
#endif
};
unsigned long x;
